JPH04149481A - Image forming device - Google Patents

Abstract

PURPOSE:To automatically correct the change of the magnification of an image on a photosensitive drum caused by positional deviation by projecting light to the non image forming area of a photosensitive body, detecting the variation of the length of the optical path of the light with the aid of the reflected light of the light and modulating a laser beam in accordance with the detected result. CONSTITUTION:This device is provided with a detection means 3a which projects the light to the non image forming area of the photosensitive body 2a and detects the variation of the length of the optical path of that light with the aid of the reflected light of that light, and laser modulation means 103-106 which modulate the laser beam in accordance with the detected result by the detection means 3a. The light is projected to the non-image forming area of the photosensitive body 2a, and the variation of the length of the optical path of that light is detected with the aid of the reflected light of that light, then the means act so that the laser beam is modulated according to the detected result. By detecting the variation of the length of the optical path of the reflected light caused by the positional deviation of the photosensitive body 2a, the modulation of the laser light is adjusted in accordance with the variation amount, and the variable power of the image accompanied with the positional deviation of the photosensitive body 2a, etc., is prevented.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an image forming apparatus that scans a photoreceptor with a laser beam and forms an image using an electrophotographic process.

[Conventional technology]

2. Description of the Related Art Conventionally, there is a color image forming apparatus that irradiates a plurality of photosensitive drums with a laser beam corresponding to each color of image data to form an image through an electrophotographic process. However, in such a device, for example, there are multiple (four in this example) corresponding to magenta, cyan, yellow, and black.
Because photosensitive drums are used, eccentricity of each of these photosensitive drums or mechanical installation errors may cause misregistration of each color in the final color image obtained on the transfer paper, resulting in color misregistration. there were. As a conventional correction method for such defects, images for each color formed by these photosensitive drums are transferred from each photosensitive drum onto a transfer belt, and a registration correction image is formed. The pattern is read with a CCD sensor, etc. Then, based on this read image, registration deviations on the photosensitive drum corresponding to each color are detected. Based on this finding,
This registration shift can be reduced by electrically correcting the timing of the image signal to be recorded, or by correcting changes in optical path length and optical path using a mirror installed in the optical path of the laser beam. ing.

[Problem to be solved by the invention]

As described above, in the conventional example described above, the registration correction image pattern formed on the transfer belt is read by a CCD sensor or the like, and registration deviations are detected and corrected. For this reason, there is a problem in that it is not possible to correct magnification changes in the horizontal scanning direction caused by optical path length changes due to eccentricity of each photosensitive drum and mechanical installation errors. FIG. 6 is a diagram showing changes in the latent image magnification on the drum surface due to positional changes of the photosensitive drum. Here, the photosensitive drum 50
1, when the laser beam 502 is scanning in the main scanning direction indicated by the arrow in the figure, when the surface of the photosensitive drum 501 changes in the direction in which the optical path length becomes shorter as shown by 504 with respect to its reference position 503. , the scanning width of the laser beam is B-B
', which is narrower than the reference width A-A'. On the contrary, if the optical path length changes in the direction shown by 505, the scanning width becomes c-c', and the reference width A-
It will be wider than A'. The present invention has been made in view of the above conventional example, and an object of the present invention is to provide an image forming apparatus that can automatically correct changes in the magnification of an image on a photosensitive drum caused by eccentricity or positional deviation of the photosensitive drum. purpose.

[Means to solve problems] In order to achieve the above object, the image forming apparatus of the present invention has the following configuration. That is, An image forming apparatus that scans a photoreceptor with a laser beam to form an image using an electrophotographic process, in which light is projected onto a non-image forming area of the photoreceptor, and the light is reflected from the photoreceptor. and a laser modulation means that modulates the laser beam according to the detection result of the detection means. [Effect]

In the above configuration, light is projected onto the non-image forming area of the photoreceptor, a variation in the optical path length of the light is detected by the reflected light of the light, and the laser light is modulated according to the detection result. works. As a result, when a change in the optical path length of the reflected light due to the positional deviation of the photoreceptor is detected, the modulation of the laser beam is adjusted according to the amount of change, and the magnification of the image due to the positional deviation of the photoreceptor is adjusted. Prevented.

【Example】

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. <Description of Laser Beam Printer (Fig. 1)> Fig. 1 is a block diagram showing the schematic configuration of the laser beam printer of this embodiment. In the figure, reference numeral 101 denotes an input unit that inputs image data from an external device such as a host computer and outputs it to the control unit 102. Reference numeral 102 denotes a control unit for controlling the entire apparatus, which outputs image data for each color input from the input unit 101 to a corresponding video signal processing unit. 103~
106 is a video signal processing unit; 103 processes magenta image data and outputs it to a magenta recording unit 107; Reference numeral 104 inputs cyan image data and outputs it to the cyan recording section 1.08. 105 processes the yellow image data and outputs it to the yellow recording section 109. 106 is a black recording unit 1 that processes black image data;
10. The configuration of these video signal processing sections is shown in FIG. Reference numerals 107 to 110 are recording units that perform recording in each color, and among these, a magenta recording unit 107 that records in magenta color is schematically shown. Here, 2a indicates a photoreceptor drum,
Reference numeral 111 indicates a semiconductor laser that outputs laser light modulated according to image data from the control unit 102. 3
a is a reflective photosensor, which includes a light emitting part that emits light;
By irradiating light onto the photoreceptor drum 2a and detecting the reflected light, it is possible to detect positional deviation, bias, etc. of the photoreceptor drum 2a. As shown in FIG. 2, these recording units 107 to 110 are arranged in a line along the transfer belt 11 in the order of image formation. FIG. 2 is a configuration diagram showing the configuration of the recording section for each color in the color laser beam printer of this embodiment. In FIG. 2, each of ρ1 to β4 represents the colors Ma (magenta), Cy (cyan), Ye (yellow), and Bk (
shows the laser beam corresponding to the image signal (black),
The irradiation is applied to the photosensitive drums 28 to 2d corresponding to magenta, cyan, yellow, and black, respectively.
An electrostatic latent image is formed on 2d. Each of 6 to 9 is a motor for rotationally driving the corresponding photosensitive drum 2a to 2d. The electrostatic latent images formed on the photoreceptor drums of each color are developed with magenta, cyan, yellow, and black toners by developing means (not shown) corresponding to the electrostatic latent images formed on the photoreceptor drums, and the developed magenta, cyan, yellow, and black The images are sequentially transferred onto recording paper conveyed on the transfer belt 11. 3
Each of 8 to 3d is a reflective photosensor, and as described above, is used to detect positional deviation of the photosensitive drums 28 to 2d. FIG. 3 shows the magenta video signal processing unit 103 of this embodiment.
FIG. 2 is a block diagram showing the configuration of FIG. Note that since the configurations of the other video signal processing units 104 to 106 are similar, only the video signal processing unit 103 is shown here. Before explaining this FIG. 3, the photosensitive drum 2a and the reflective photosensor 3 of the magenta recording section 107 shown in FIG.
The operation of a will be explained. Incidentally, here, the magenta recording section 10
Although only the No. 7 photosensitive drum 2a is shown, the same applies to the photosensitive drums of the recording sections of other colors. FIG. 4(B) is a top view of the photosensitive drum 2a viewed from above, and as shown in the figure, the photosensitive drum 2a has a light reflecting area 4 at the end in the circumferential direction that reflects light, and a The photosensitive area 5 occupies most of the surface of the photosensitive area. As shown in FIG. 4(A), light is incident on this light reflection region 4 from the reflective photosensor 3a (ρ5), and the reflected light (ρ6)
is detected by the photosensor 3a. At this time, if the optical path and optical path length of the incident light 459 and the reflected light β6 change due to eccentricity of the photosensitive drum 2a and mechanical installation error, the detection level of the reflected light intensity of the reflective photosensor 3a changes. This output is the sample hold (S/H) shown in Figure 3, which will be described later.
) is input to the amplifier 16. This sample hold (S
/H) The amplifier 16 once per horizontal scanning period (IH),
Sample and hold is performed according to the gate signal (LSYNC), and the voltage is amplified to a predetermined level. The level signal 202 sampled and held in this manner is then input to the voltage controlled oscillator 17 and converted into a frequency signal (RCLK) 203 corresponding to the voltage level. This clock (RC
LK) is used as a read clock for the FIFO memory 18, and is used to read a video signal (VIDEOOUT) with a predetermined modulation factor with respect to the input video signal (VIDEOIN).
) is output as This video signal undergoes predetermined signal processing and is input to a laser drive circuit (not shown) to drive the semiconductor laser 111. In this way, an electrostatic latent image is formed on the photosensitive drum 2a by the laser beam. In FIG. 3, 3a is a photosensor, and a light emitting element 31
and a light receiving element 32. The signal thus detected is input to the sample and hold amplifier 16, and a sampled and held level signal 202 is output. The voltage controlled oscillator 17 is a circuit that performs voltage-frequency conversion, and generates a clock signal 203 with a frequency corresponding to the voltage value of the signal 202.
Output. This clock (RCLK) signal 203 is F
The data is input to the IFO memory 18, and the transfer rate of video data from the control unit 102 is changed. This timing is shown in the timing chart of FIG. 5, which shows the frequency change of the FIFO memory read clock in accordance with the output level change of the reflective photosensor due to eccentricity of the photosensitive drum and mechanical installation error. As is clear from this figure, when the output level of the reflective photosensor increases, that is, the optical path length becomes shorter (when the image is reduced), the output clock signal 203 of the voltage controlled oscillator 17
frequency (VCXO) decreases. This corrects the image becoming smaller. Conversely, when the output level of the reflective photosensor decreases, that is, when the optical path length becomes long (when the image is enlarged), the frequency (VCXO) of the output clock signal 203 of the voltage controlled oscillator 17 increases. This speeds up the output of image data and prevents the image data formed on the photosensitive drum from being enlarged. This principle will be explained with reference to FIG. 6. As shown by BB' in FIG. When the drum surface approaches the reflective photosensor due to a positional change of the photosensitive drum 501, the optical path length of the laser beam 502 becomes shorter, and the electrostatic latent image on the photosensitive drum 501 is reduced in the horizontal scanning direction. At this time, the optical path length between the light-emitting and light-receiving elements of the reflective photosensor also becomes shorter, so the detection level also increases.As a result, the input signal level to the voltage-controlled oscillator 17 increases, and its output frequency increases. That is, FIFO memory 1
The read clock (RCLK) frequency of No. 8 becomes lower. As a result, the image recorded by the image data read from the PIF 018 is enlarged, and as a result, it is possible to correct image reduction due to variations in optical path length. On the other hand, as shown in c-c', when the drum surface of the photosensitive drum 501 moves away from the reflective photosensor, the optical path lengths of the laser beams ρ1 to 4 become longer. This results in
The latent image on the photosensitive drum 501 is expanded in the horizontal scanning direction. However, in this case, the detection level of the reflective photosensor becomes small (contrary to the above), and accordingly, the output of the voltage controlled oscillator 17, that is, the read clock (RCLK) frequency of the FIFO memory 18 becomes high. This results in
Since the image data is read out at high speed and the image formed by the image data thus read out changes in the direction of reduction, it is possible to correct the enlargement of the image due to the positional fluctuation of the photosensitive drum 501 as a whole. As described above, according to this embodiment, the image magnification in the horizontal scanning direction is corrected by detecting a change in the laser beam optical path length due to a change in the photosensitive drum position and varying the memory read clock for image data accordingly. be able to. As a result, even if a positional shift or the like of the photoreceptor drum occurs, it is possible to prevent the image from being enlarged or reduced. <Other Embodiments> In the above embodiments, the voltage controlled oscillator (VCXO) 17, which varies the crystal oscillation frequency with respect to the analog input voltage, was used as an example of the voltage controlled oscillation means.
The present invention is not limited to this. For example, as shown in FIG. 7, a detection signal from the photosensor 3a is input, and a plurality of comparators

Claims (3)

[Claims] (1) An image forming apparatus that scans a photoreceptor with a laser beam to form an image using an electrophotographic process, which projects light onto a non-image forming area of the photoreceptor and generates reflected light of the light. An image forming apparatus comprising: a detection means for detecting a variation in the optical path length of the light; and a laser modulation means for modulating the laser light according to a detection result of the detection means. (2) The laser modulation means includes a holding means for holding image data to be recorded, a changing means for changing the reading speed of the image data held in the holding means according to the detection result of the detecting means, and 2. The image forming apparatus according to claim 1, further comprising laser driving means for driving a laser to generate laser light by driving a laser according to the image data read out from the holding means. (3) The image forming apparatus according to claim 1, wherein the detection means detects the variation in the optical path length in synchronization with each horizontal scanning signal.